At some point after our toon gets past the 400 signet mark, signets of learning do nothing much besides saving it up for your next toon or selling it on trade.
If you're reading this, what do you think about say 50 signets = 1 random SU? Or maybe a 100.
Or even a vendor to sell shrines but using signets as a currency. 10 or 20 signets for a specific shrine perhaps?